Through four games, the Celtics have alternately shown signs of championship-caliber competence and non-contender nonchalance.

They have failed to follow the game plan, defensive mix-ups allowing the easiest of opponent scores and offensive mess-ups leading to poor shot selection or turnovers. It has not been clear whether the team being out of synch has led to lethargy, or the opposite.

Two successive wins against Washington have left the Celtics with a 2-2 record. But the results were received with qualified optimism, since the Wizards were missing key players — as will be the case when the Celtics host the Andrew Bynum-less Philadelphia 76ers Friday night.

Kevin Garnett preached patience after Wednesday’s game.

“I think we can improve,” said Garnett. “Obviously, there are parts of the game, you can say we can improve. I thought we started the game off strong, tried to get it back the second half.

“I’m getting tired of saying this, sound like a broken record, but consistency — if we’re going to be a great team, not a good team, it’s going to be how consistent we are. Until we are . . . like I said before, we’re still working and that’s what we are. I know it looks crummy at times, but just stay with us.”

The Celtics have been at their best when strategy is simplified and the transition game is flowing.

They have suffered major breakdowns in half-court sets, though. Trying to protect a 2-point lead over the Wizards in the final seconds, the Celtics allowed Chris Singleton an uncontested drive from the top of the circle for a dunk, then took a timeout and failed to execute a play, leaving Rajon Rondo to launch a 3-point attempt
off the dribble. The Celtics finally got into a flow for a 100-94 overtime victory.

In the overtime, the Celtics found an effective combination with a lineup totaling 57 years of experience. Brandon Bass, who had 6 points during regulation, finally focused in the final minutes, breaking a tie and personally extending the lead to 5 points over a 1:47 span.

“Veterans who have been in the thick and know how to win,” Garnett said.

Jason Terry scored 16 points, his most since joining the Celtics, but did not take a shot in overtime.

“You want your best players in there, and I thought he did small things, communicating, rotating, in the latter parts of the game,” Garnett said of Terry.

But coach Doc Rivers had to go with newcomers and youngsters during regulation, testing his patience.

“I thought we were supposed to do that [trapping defense] at the beginning of the game, and that’s why I was so frustrated early,” Rivers said. “Whenever [Kevin] Seraphin got the ball we were going — I wasted two timeouts to remind our guys to go with speed and we were going, but we were trying to play that cat-and-mouse trap game, which guys in the NBA are too good for that. You can do that in college but not in this league.

“So when we talked about it at halftime, I thought we came out and did it, and forced a ton of turnovers.”

Bass and Terry led the way for the Celtics reserves. Though the Boston bench was outscored, 53-41, this was the first time it showed signs of its potential firepower. Chris Wilcox,
who scored just 2 points in the opening three games, produced 6 points, 2 rebounds, and a blocked shot in 3:41 in the third quarter.

“This was good for the bench, we stuck to [defensive] assignments and, offensively, we were more aggressive,” Terry said. “Now, we have to get it more consistent.”